Transmission Fluid
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2nd Gear
Joined: Dec 2025
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Transmission Fluid
2004 F250 Automatic, always used Ford SP fluid. The transmission has about 200,000 miles on it. It was running perfect when I sold it, the new owner added a quart of Castro TRANSMAX DEX/MERC, and now the engine quits as soon as you put it in gear. Could this fluid cause the solenoids on the torque converter to stick causing it to stay locked up?
Laughing Gas
Joined: Oct 2018
Posts: 1,004
Likes: 85
From: San Diego
Google AI says the following:
Castrol Transmax DEX/MERC is a multi-vehicle automatic transmission fluid (ATF) designed for older Ford and General Motors vehicles, meeting both DEXRON-IIIH and MERCON specifications for smooth shifting, enhanced durability, and improved performance in older transmissions, but should not be used in newer applications requiring DEXRON-VI, MERCON V, or MERCON SP. It's an excellent choice for extending the life of older automatics and can also serve in power steering systems where MERCON fluid is specified.
So to test the theory; drain out all fluid including torque convertor, and refill with the proper Motorcraft brand only.
Follow Mark Kovalsky's tutorial: Read it twice first.
https://www.ford-trucks.com/articles...-transmission/
Castrol Transmax DEX/MERC is a multi-vehicle automatic transmission fluid (ATF) designed for older Ford and General Motors vehicles, meeting both DEXRON-IIIH and MERCON specifications for smooth shifting, enhanced durability, and improved performance in older transmissions, but should not be used in newer applications requiring DEXRON-VI, MERCON V, or MERCON SP. It's an excellent choice for extending the life of older automatics and can also serve in power steering systems where MERCON fluid is specified.
So to test the theory; drain out all fluid including torque convertor, and refill with the proper Motorcraft brand only.
Follow Mark Kovalsky's tutorial: Read it twice first.
https://www.ford-trucks.com/articles...-transmission/
Last edited by marksman76; Dec 10, 2025 at 11:27 AM.
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,714
Likes: 2,640
From: SE Florida
2004 F250 Automatic, always used Ford SP fluid. The transmission has about 200,000 miles on it. It was running perfect when I sold it, the new owner added a quart of Castro TRANSMAX DEX/MERC, and now the engine quits as soon as you put it in gear. Could this fluid cause the solenoids on the torque converter to stick causing it to stay locked up?
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